Opens with music.
Narrator: Because of this sound...your watch might be out of whack on Saturn.
Natural sound of radio emissions from Saturn
Narrator: I'm Jane Platt with a podcast from JPL ? NASA's Jet Propulsion Laboratory in Pasadena, California. If you could somehow stand in the murky, gaseous environment of Saturn, you might find it hard to keep track of time. Here to explain why is Dr. Don Gurnett of the University of Iowa. He's principal investigator on the radio and plasma wave science experiment on NASA's Cassini spacecraft. Don, what exactly is that sound?
Gurnett: That sound that you heard is the sound of radio emissions from Saturn. And I think you could very definitely hear that beat. The sound that you're hearing was speeded up considerably. We had 5 days that were played in only 15 seconds. And the beat period you could hear, that is the rotation of Saturn. It essentially gives us the length of the day at Saturn.
Narrator: So that is actually the sound of Saturn rotating.
Gurnett: Yes it?s the sound of Saturn rotating. And the puzzling thing is when we first measured the rotation rate using this radio technique with Voyager in 1980, and it was 10 hours and 39 minutes. But with Cassini, which arrived at Saturn in 2004, the period had increased by 6 minutes, which has really been a big puzzle because a big planet like that really can't change its rotation period.
Narrator: So that'd be kind of like all of a sudden Earth, instead of having a 24-hour day would have a 24-hour and 6 minute day?
Narrator: So how do you account for this?
Gurnett: Well, we've come up with a theory that the moon Enceladus, Enceladus has geysers, it emits gas into the region around Saturn, forms a big donut of neutral gas around Saturn, and that this gas gets ionized and picked up by the rotating magnetic field of Saturn, and actually slows down the magnetic field rotation rate. Essentially these particles produce a drag force on the magnetic field and force the magnetic field to rotate at a slower rate than Saturn.
Narrator: So are you actually, with these radio emissions, are you measuring the length of time of a Saturn day, or the donut around Saturn?
Gurnett: Well, we're measuring the rate at which the magnetic field rotates, and we believe that that magnetic field slips slightly with respect to Saturn. So we're not actually measuring the internal rotation period of Saturn.
Narrator: Anything else that you think is interesting about your latest findings, which are being reported in the journal Science?
Gurnett: Well, it's kind of an exotic idea. There's this gas from Enceladus-- we didn?t know about that even a year ago. And so there's some really new developments, and I'm sure there's more things that we need to research and understand about how this works, but its kind of a new, surprising result.
Narrator: One last thing, I think I always like to clarify, the sound that we're hearing--if you were somehow able to be near Saturn, you wouldn?t be hearing that?
Gurnett: No, you would not hear that sound. This is the sound picked up by a radio receiver just like, say, your car radio, and these charged particles at Saturn that are controlled by the magnetic field, they make this radio noise. Also, just like your car radio, we're actually detecting a radio signal up at a frequency of a few hundred kilohertz, but its being shifted down so you can hear it in the audio range.
Narrator: Alright, well thank you so much for your time, Don, I appreciate it.
Gurnett: Yes, you're welcome.
Narrator: More information on Cassini is at http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov/ . You've been listening to a podcast from NASA's Jet Propulsion Laboratory.